Lateral ankle ligament injury is one of the most commonly occurring ligament injuries, especially in sports-related activities. It has been estimated that there are about 23,000 inversion injuries of the ankle in this country everyday. However, due to inadequate diagnoses and improper treatments, about 10-30% of patients will progress to chronic symptoms which may eventually lead to hindfoot osteoarthritis. Improvement of diagnoses and treatments would benefit a great number of people suffering from this problem. For years, diagnosis of ankle ligament injuries has been a difficult problem for a foot surgeon. The most challenging question is how to identify the injured ligament(s), especially for the chronic patients. Classical stress testing only has about 50% accuracy in differentiating the isolated anterior talofibular ligament (ATFL) injury and the combined ATFL and calcaneofibular ligament (CFL) injury, the two most common lateral ankle injuries comprising 86% of all ruptures of the ankle ligaments. The major obstacle to injury assessment is anatomical variation among individuals, leading to no clear criteria to indicate the extent to which the ligament(s) is injured. This uncertainty not only affects the decision of treatment procedures, but more importantly, the treatment outcomes. The long-term goal of this project is to develop a new diagnostic technique for ankle ligament injury. More specifically, in this three-year period of time we will perform the laboratory testing which is necessary to validate this method. The technique consists of two novel aspects: 1) The diagnosis will be based on patterns of foot motion sensitive to injuries and using curve comparisons as opposed to limited foot position tests which use point estimation in stress testing, and 2) statistical trend analysis will be introduced into this area for the first time to analyze the curve patterns quantitatively. Preliminary studies have shown that the pattern comparison is much more sensitive than the point comparison. This provides us the confidence to further carry out this project to systematically test the following hypotheses: H1: Intact foot, foot with isolated ATFL rupture, and foot with combined ATFL and CFL rupture have distinct foot motion patterns. H2: Pattern comparison is much more precise in differentiation between the isolated ATFL rupture and the combined ATFL and CFL rupture that point comparison in stress testing. H3: Based on foot motion pattern analysis, there exist optimal manipulations which are more sensitive than the others for such a diagnosis.